The present invention relates to a method for forming a field oxide film on a semiconductor device, and more particularly, to a method for forming a field oxide film on a semiconductor device using a silicon epitaxial layer to improve a Shallow Trench Isolation (STI) process.
FIGS. 1A to 1E illustrate, in sectional views, a conventional method for forming a field oxide film on a semiconductor device. As shown in FIG. 1A, a layer of pad oxide film 12, a layer of silicon nitride film 14, and a layer of photoresist film 16 are formed on a silicon substrate 10. The photoresist film 16 is selectively exposed and developed to form a photoresist pattern 16a, as shown in FIG. 1B. The silicon nitride film 14 and the pad oxide film 12 are typically removed sequentially using the photoresist pattern 16a as a mask to form a thermal oxidation mask comprising the silicon nitride film 14a and the pad oxide film pattern 12a. As shown in FIG. 1C, the exposed silicon substrate 10 is then removed to a desired depth using the thermal oxidation mask to form a channel 18, after which the photoresist pattern 16a is removed.
Subsequently, as shown in FIG. 1D, an oxidation process is performed to form rounded corners of the channel 18, and a silicon oxide film 20 is formed on the exposed surface of the channel 18. The entire surface is then coated with a field oxide film 22, e.g., by a Chemical Vapor Deposition (CVD) method, to cover the channel 18. As shown in FIG. 1E, the field oxide film 22 is then selectively removed and planarized, e.g., by a Chemical Mechanical Polishing (CMP) process, using the silicon nitride film pattern 14a as an etching stop film. In a subsequent process, the silicon nitride film pattern 14a is removed by a wet etching process.
However, conventional methods for forming a field oxide film on a semiconductor device have several limitations. For example, the area of active silicon region is reduced during the oxidation process for making rounded channel edges (i.e., corners), typically in the amount of about 0.01 xcexcm width. This reduction of the active silicon region affects the operational characteristics of a cell process significantly, especially for cells having a design rule of 0.1 xcexcm or less. For example, in a cell having an active region width of about 0.1 xcexcm, the width of the active region can be reduced to about 80 nm or less, which reduces the cell current by about 20% or more.
The present invention provides a method for forming a field oxide film on a semiconductor device. Methods of the present invention substantially obviate one or more problems in conventional field oxide film formation methods.
An object of the present invention is to provide a method of producing a field oxide film on a semiconductor device and minimize the amount of active region reduction during an STI process.
Another object of the present invention is to provide a method of producing a field oxide film on a semiconductor device and minimize the amount of cell current reduction in the resulting semiconductor device.
Yet another object of the present invention is to provide a method of producing a field oxide film on a semiconductor device and reduce the ohmic contact during self-alignment contact, thereby improving the circuit operational speed.
Accordingly, the present invention provides a method for forming a field oxide film on a semiconductor device comprising the steps of:
producing a thermal oxidation mask on a silicon substrate;
producing a channel on said silicon substrate using said thermal oxidation mask;
producing a silicon epitaxial layer on the surface of said silicon substrate channel;
producing a spacer mask on side surfaces of said thermal oxidation mask;
producing a smooth edged silicon epitaxial layer near the interface between said spacer mask and said silicon epitaxial layer; and
producing a field oxide film on said silicon substrate.
In one embodiment of the present invention, the thermal oxidation mask comprises silicon nitride film. The thermal oxidation mask can further comprise a pad oxide film disposed between the silicon substrate and the silicon nitride film.
In another embodiment of the present invention, the spacer mask comprises silicon oxide.
The smooth edged silicon epitaxial layer producing step can include oxidizing the silicon epitaxial layer under conditions sufficient to form a layer of silicon oxide film on the silicon epitaxial layer and the smooth edged silicon epitaxial layer near the interface between the spacer mask and the silicon epitaxial layer. Preferably, the thickness of the silicon epitaxial layer is from about 50 to about 100 xc3x85.
The spacer mask producing step can comprise coating the silicon substrate with a silicon oxide film and removing the silicon oxide film under conditions sufficient to produce the spacer mask. Preferably, the silicon oxide film coating thickness is from about 50 to about 100 xc3x85.
The field oxide film producing step can include producing a layer of field oxide film material on the silicon substrate and planarizing the field oxide film material using the thermal oxidation mask, e.g., silicon nitride film, as an etching stop film. Preferably, field oxide film material is planarized using a CMP process.
Another aspect of the present invention provides a method for forming a field oxide film on a semiconductor device comprising the steps of:
forming a thermal oxidation mask on a silicon substrate, wherein said thermal oxidation mask comprises silicon nitride film;
forming a channel on the exposed regions of said silicon substrate;
forming a silicon epitaxial layer on the surface of said silicon substrate channel;
forming an oxide film spacer mask on side surfaces of said thermal oxidation mask;
forming a smooth edged silicon epitaxial layer near the interface between said oxide film spacer mask and said silicon epitaxial layer by oxidizing the exposed silicon epitaxial layer; and
forming a field oxide film on said silicon substrate.